Mary asks about a relationship with her ex-husband and her father-in-law from 30 years ago.  She feels it is behind her now but wants to know how to deal with her sister-in-law.
You cannot make someone else’s truth for them yours.
In other words, Mary wants to be heard and seen and understood by this sister-in-law but that is not possible at this time.  So it is best if she simply be her own truth, if she has accepted the forgiveness of others and moved forward.
Do not plague yourself with this my dear.  There is a reason you have moved forward.  Accept it…and love yourself.